CGC

1
The Little Bang
Art due to Tetsuo Hatsuda and Steffen Bass (with
some artistic interpretation)
CGC
Initial Singularity
Glasma
sQGP
Hadron Gas
2
Strong correspondence with cosmology. How can
ideas be tested? What are the new physics
opportunities?
3
The Initial Wavefunction for High Energy
Baryon 3 quarks 3 quarks 1 gluon .. 3 quarks
and lots of gluons
4
Density of Gluons Grows
becomes weak
Color Glass Condensate
Successes Geometric scaling in DIS Diffractive
DIS Shadowing in dA Multiplicity in AA Limiting
fragmentation Long range correlations Total cross
section Pomeron, reggeon, odderon
Break down of factorization of pp to ep?
Saturated hot spots?
5
The Initial Singularity and the Glasma
The hadrons pass through one another
Topological charge density is maximal Anomalous
mass generation In cosmology Anomalous
Baryogenesis
Before the collision only transverse E and B CGC
fields Color electric and magnetic monopoles
Almost instantaneous phase change to longitudinal
E and B
Production of gluons and quarks from melting
colored glass
6
The Initial Singularity and the Glasma
Before collision, stability
After collisions, unstable
Quantum fluctuations can become as big as the
classical field Quantum fluctuations analogous to
Hawking Radiation Growth of instability generates
turbulence gt Kolmogorov spectrum Analogous to
Zeldovich spectrum of density fluctuations in
cosmology Topological mass generation
Interactions of evaporated gluons with classical
field is g x 1/g 1 is strong Thermalization?
7
Fluctuations in The Initial Singularity
During inflation Fluctuations on scale larger
than even horizon are made Late times Become
smaller than even horizon gt Seeds for galaxy
formation
Fluctuations over many units in rapidity in
initial wavefunction
8
Instabilities driven by momentum anisotropy
9
The sQGP
Good agreement of well thought out hydro
computations with radial and elliptic flow data
Energy density is high enough
Very large energy loss of jets
The evidence is strong that one has made a system
of quarks and gluons which is to a good to fair
approximation explained by a Quark Gluon Plasma
10
More evidence
Is
its lower bound
?
Conclusion depends on initial conditions?
Coalesence models reproduce v2 at intermediate
pt. Do they work too well? Energy conservation?
Water
Do we really need huge cross sections in
transport to reproduce flow data?
Has led some to suggest that we live in the best
of all possible worlds!
11
Hydro plus CGC Initial Conditions Good
description of multiplicity and pT distributions
12
Hydro CGC Jet quenching good description of
jets (except for heavy quarks!)
13
Good description of v_2 when dissipative effects
in hadronic matter are included CGC Initial
conditions without viscosity in QGP do less well
Can and will do better Next generation of
hydro, e. g. Spherio Fully 3-d with
viscosity Need more than just running codes and
fitting data!
We do not yet properly treat Thermalization.
Initial conditions. Viscosity in QGP not yet
treated in fully consistent way Hadronization and
coalesence not fully self consistent
14
CGC Initial Conditions? Large parton cross
sections not required for flow. Thermalization
through mutligluon interactions? Plasma
Instabilities? Viscosity effects are unknown,
computation is theoretical challenge.
Viscous Hydrodynamics Becoming practical
15
Glasma
Definition The matter which is intermediate
between the Color Glass Condensate and the Quark
Gluon Plasma It is not a glass, evolving on a
natural time scale It has components which are
highly coherent,
Components which are particle like
Components of strength in between
Initially it has large longitudinal color
electric and color magnetic fields, and maximal
topological charge density
16
Choose A 0 in backward light cone. In left and
right halves, pure gauge. Discontinuity across
light cone to match color charge sources on light
cone Field is not pure gauge in forward lightcone
Physical motivation Renormalization group
description. In center of mass frame, degrees of
freedom with
are coherent fields. Larger y are sources
17
Before the collision, two sheets of mutually
transverse color electric and color magnetic
fields. Boosted Coulomb fields Random in
color Thickness of sheets is
18
Initial fields
In radial gauge,
the fields in the forward light cone are
Assume boost invariant solution
19
Boundary conditions are determined by solving
equations across the light cone Infinitesmally
after the collision there are No transverse
fields Longitudinal magnetic and electric fields
20
These fields have a local topological charge
density Chern-Simons charge
The Chern-Simons charge density is maximal!
and has a transverse correlation length
21
How do the sources of color magnetic and color
electric field arise?
In forward light cone, the vector potential from
one nucleus can multiply the CGC field from the
other. Equal and opposite densities of charge
22
However Glasma fields are initial conditions,
not a solution to time independent equation of
motion
Unlike the constant field where there is no
magnetic field
23
The Lund model made the daring proposal that
there were longitudinal electric fields which
decay by pair production There is also a
longitudinal magnetic field It can also decay by
rearrangement of the charge in the classical
field (classical screening) which is naively
dominant
Kharzeev and Tuchin and Janik, Shuryak and Zahed
made the daring proposal that particles are made
by decay of Chern-Simons charge. Both are
correct! They are included in the color glass
initial conditions!
The matter which is this melting glass, or
hadronizing strings or sphaleron decays is the
Glasma
24
The Glasma has three components Coherent
classical fields Hard particles Degrees of
freedom which can be described as either hard
particles or coherent fields
The Glasma has mostly evaporated by a time
During this time, scattering among the hard modes
(parton cascade) is not important
25
Interactions in the coherent fields takes place
on a scale of order 1/Qs Because of coherence,
interactions of hard particles with the classical
fields, g x 1/g 1 Also take place on a time
scale 1/Qs Very rapid strongly interacting system
But boost invariance is a problem, as this does
not allow longitudinal momentum to become
thermalized Important for two reasons Almost
certainly instabilities of the hard-soft coupled
system under boost non-invariant
perturbations The local topological charge wants
to decay, and this is easiest with a boost
non-invariant distribution
26
Consequence of nonzero Chern-Simons Charge
Vorticity Generation
Positively charged particle accelerates along E,
rotates in clockwise direction Negatively charged
particle accelerates along -E, Rotates in
anticlockwise direction Net vorticity generation
Physical origin of t Hooft anomaly
27
Generating the Initial Distribution of
Fluctuations with Kenji Fukushima and Francois
Gelis
28
In the Classical Limit
Writing
And expanding the action for small r
29
Need Wavefunction Infinitesimally in Forward
Lightcone
Backward lightcone is free field theory Source
are delta functions along the light cone Answer
is that in terms of transverse field Gaussian
shifted around sum of fields in backward light
cone Longitudinal field determined by Gausss law
Spectrum of Initial Fluctuations is known!